1. Field of the Invention
The present invention relates to a camera which includes an electronic flash and a shake detector, and, more particularly, to a camera which reduces time lag from a time after completion of a charging operation of a stroboscope to a time of an exposure operation by completing the charging operation of the electronic flash and starting a detection operation of camera shake at predetermined timings.
2. Description of the Related Art
In a single-lens reflex camera including a through-the lens (TTL) finder, the finder image is an image obtained after passage through a:camera shake correcting lens, so that the result obtained through the camera shake correcting lens can be confirmed in real time. Therefore, in a conventional single-lens reflex camera including a vibration isolator, the power supply to a camera shake detecting system is turned on while an ON/OFF switch for correcting camera shake is turned on, and the correcting lens is driven while a release switch is pressed halfway, that is, while a switch SW1 is turned on. In this state, the image obtained after correction by the camera shake correcting lens can be directly confirmed through the finder.
A driving circuit of a camera shake correcting lens and a camera shake detecting, system in such types of cameras are disclosed in U.S. Pat. Nos. 5,153,633, 5,637,860, and 5,864,722. In U.S. Pat. No. 5,153,633, the process after completion of a release operation carried out after a switch SW1 has been pressed is disclosed in U.S. Pat. No. 5,637,860, when a main switch SW is turned on, electrical power is supplied to a camera shake sensor, and correction of camera shake is started by depressing a release switch. When a predetermined period of time elapses without a release operation being carried out, the supply of electrical power to the camera shake detector (sensor) is stopped. In U.S. Pat. No. 5,864,722, correction of camera shake is started, and then is stopped after the passage of a predetermined amount of time.
The start-up time of a camera shake detecting sensor required for it to start performing a proper (reliable) output operation is in the range of from a few hundred milliseconds to a few seconds. Similarly, an integrator circuit of signal processing means requires a certain amount of time to operate stably. Therefore, when the operator starts/turns on the power supply after the release switch has been pressed, a problem arises in that a driving operation for performing precise correction cannot be carried out immediately after the release operation. Consequently, in these prior art systems, electrical current is supplied to the detector/sensor as early as possible and for a long period of time, and the driving operation of the correcting lens, which requires a large amount of electrical current, is minimally carried out only to the extent required.
In a lens shutter camera, whose finder and shooting optical system are separately formed, the effects of the camera shake correcting lens thereof cannot be confirmed through the finder, so that it is not necessary to drive the camera shake correcting lens while the release switch is pressed halfway, that is, while switch SW1 is pressed. In other words, it is not necessary to drive the camera shake correcting lens at any time other than a time immediately before and immediately after an exposure operation.
However, the battery capacity or the number of batteries used in a lens shutter camera is smaller than the capacity/number used in a single-lens reflex camera. Therefore, although a driving operation of the camera shake correcting lens, which requires a large amount of current, only needs to be carried out immediately before and immediately after an exposure operation, the amount of electrical power consumed by the camera shake detecting system becomes appreciable compared to the amount of electrical power consumed by other circuits of the lens shutter camera, when electrical power is supplied to the camera shake detecting system by turning on a main switch, and then is stopped after a certain period of time. Consequently, the loss of electrical power is large, thereby making it necessary to optimize the method of supplying electrical power.
For example, in a compact camera having an electronic flash (stroboscope) circuit, the battery voltage is excessively reduced during a charging operation of the electronic flash. A method of controlling the power supply to a camera shake detecting system during a charging operation of the electronic flash is disclosed in, for example, U.S. Pat. No. 5,210,563. U.S. Pat. No. 5,210,563 proposes not to use the output of the camera shake detecting system during a charging operation of the electronic flash because the reliability of the output cannot be maintained due to changes in the power supply voltage supplied to the camera shake detecting system during the charging operation of the electronic flash. For example, Japanese Patent Laid-Open No. 7-281241 proposes to prohibit a charging operation of the electronic flash during operation of the camera shake detecting system or to stop the operation of the camera shake detecting system when a determination is made that the battery used for making the stroboscope emit light is uncharged.
However, lens shutter cameras are becoming smaller, like the battery used, so that the load supplying capability of the power supply circuit cannot be made very large. Therefore, when the load supplying capability of the power supply circuit is taken into consideration, a method of restricting the amount of electrical power consumed by stopping the operation of the camera shake detecting system as a result of turning off the power supply to the camera shake detecting system during a charging operation of the electronic flash may be considered. For example, there is a sequence of steps for stopping operation of the camera shake detecting system by turning off the power supply to the camera shake detecting system during a charging operation of the electronic flash. More specifically, in this sequence, after an operation of the release switch, photometric operations and distant measurement are carried out. Then, after a determination has been made that the electronic flash needs to be charged, the power supply to the camera shake detecting system is turned off in order to charge the electronic flash. After completion of the charging operation, the power supply to the camera shake detecting system is turned on again. Using this method, it is possible to overcome a problem that the amount of electrical power becomes insufficient to operate the entire camera due to a reduction in the power supply voltage caused by the charging operation.
However, as described above, it is known that the start-up time required for the camera shake detecting sensor to start performing a proper (reliable) output operation is in the range of from a few hundred milliseconds to a few seconds, and that the integrator circuit and the filter circuit of the signal processing means require a certain amount of time to operate stably. Therefore, when the power supply to the camera shake detecting system is turned on after completion of a charging operation of the electronic flash, the camera shake detecting system requires time to operate stably after the completion of the charging operation of the electronic flash. Consequently, the period of time required from the time the release switch is actually pressed to the time the shutter is actually released becomes long. This period of time needs to be made shorter to improve efficiency of operation of the camera.
According to one aspect of this invention, by starting the supply of electrical power to a camera shake detecting system before a charging operation of a capacitor used to cause an electronic flash (stroboscope) to emit light is completed, the camera shake detecting system is brought into a state allowing it to perform a stable output operation when a charging operation of the electronic flash is completed. Therefore, camera shake is corrected using the detection results of the camera shake detecting system after a release switch has been pressed, thereby making it possible to reduce time lag before an exposure operation can be performed.
According to another aspect of this invention, when a charging voltage of a capacitor used to cause an electronic flash to emit light is equal to or less than a predetermined voltage level which is less than a voltage at a time a charging operation is completed, the supply of electrical power to a camera shake detecting system is stopped in order to make it possible to ensure the provision of a power supply voltage which allows stable driving of circuits other than that of the camera shake detecting system.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.